1. Field of the Invention
This invention relates generally to the production of a p-alkyltoluene or a 4,4'-alkylmethylbiphenyl and more particularly concerns the highly selective production of p-xylene or p-ethyltoluene by the transmethylation of benzene, toluene or ethylbenzene or the production of 4,4'-dimethyl- or -methylethylbiphenyl by the transmethylation of biphenyl, 4-methylbiphenyl or 4-ethylbiphenyl.
2. Description of the Prior Art
Dialkylbiphenyls are useful as high temperature heat transfer media. Dialkylbiphenyls, as well as dialkylbenzenes, are also desirable feedstocks for oxidation to the corresponding biphenyl or benzene dicarboxylic acids, which in turn are monomers that are known to be useful for the preparation of a variety of polymers. A known conventional process for producing a benzene dicarboxylic acid or a biphenyl dicarboxylic acid comprises the oxidation of a dialkylbenzene or a dialkylbiphenyl, respectively, with oxygen in the liquid phase in an acetic acid solvent at an elevated temperature and pressure and in the presence of a catalyst comprising cobalt, manganese and bromine components. In such cases, it is highly desirable that the alkyl groups on the benzene or biphenyl ring are methyl or ethyl.
Thus, there is a need for p-dialkylbenzenes and 4,4'-dialkylbiphenyls and for highly selective processes for making specific p-dialkylbenzenes or 4,4'-dialkylbiphenyls. Because of the great difficulty and expense of separating one p-dialkylbenzene or one 4,4'-dialkylbiphenyl from its other dialkylbenzene isomers or other dialkylbiphenyl isomers, respectively, methods for producing a specific p-dialkylbenzene or a specific 4,4'-dialkylbiphenyl in high purity and quality are especially desirable. One such method is disclosed in Japanese Kokai Patent Application Publication No. 62-252733 (Nov. 4, 1987) and is a process for the transethylation of biphenyl with an ethylbenzene or ethyltoluene to form monoethylbiphenyl and diethylbiphenyl in the presence of a Friedel-Crafts catalyst, such as aluminum chloride at 70.degree.-150.degree. C. This published Japanese patent application discloses that reaction temperatures of less than 70.degree. C. delay the reaction rate. The ring positions of the ethyl substituents in the ethylated biphenyl products are not disclosed. Suitable ethylbenzenes and ethyltoluenes include ethylbenzene, diethylbenzene, triethylbenzene, tetraethylbenzene, other ethyl-substituted benzenes, ethyltoluene diethyltoluene and other ethyl-substituted toluenes. Polyethylbenzenes containing relatively small amounts of monoethylbenzene, triethylbenzene and tetraethylbenzene can also be used advantageously.
Japanese Patent Application 261336, published on Oct. 18, 1989, discloses a method for the preparation of ethyldiphenylethane or diethyldiphenylethane by the transethylation of diphenylethane with polyethylbenzene(s) in the presence of a Friedel-Crafts catalyst at 0.degree.-150.degree. C. Preferred catalysts are aluminum chloride, aluminum bromide and boron trifluoride. Transethylation of 1,1-diphenylethane by this method produces either 1-phenyl-1-ethylphenylethane, 1-phenyl-1-diethylphenylethane or 1,1-bis(ethylphenyl)ethane. The ring positions of the ethyl substituents in the ethylated products are not disclosed.
With regard to a different aromatic ring system, Olah et al., "Alkylation of Naphthalene with Alkyl Halides," Journal of American Chemical Society, 98:7, pages 1839-1842 (Mar. 31, 1976), disclose that theretofor there was no clear understanding of directive effects and selectivities for the Friedel-Crafts alkylation of naphthalene. Olah et al. discloses poor selectivities and/or low conversions for the direct methylation of naphthalene or 2-methylnaphthalene using simple methylating agents such as methyl halides or methanol to provide beta-substituted products such as 2,6-dimethylnaphthalenes.
Since then, Japanese Kokai Patent Application Publication No. 61-83137 (Apr. 26, 1986) discloses a synthesis involving the transalkylation of naphthalene or a 2-methylnaphthalene in the presence of an aluminum chloride catalyst at 0.degree.-35.degree. C. in the liquid phase to produce a 2,6-dialkylnaphthalene. Suitable alkylating agents are disclosed as including durene, diethylbenzene, triethylbenzene, triisopropylbenzene, isopropylxylene, and dibutylbenzene. The reported results indicate a relatively low degree of selectivity for the formation of specific stated that the disclosed alkylation method must be performed at 0.degree.-35.degree. C., preferably room temperature, and that the higher the reaction temperature, the lower the selectivity for beta-alkyl-substituted naphthalene and especially 2,6-dialkylnaphthalene. In addition, although this patent application publication specifically mentions durene (1,2,4,5-tetramethylbenzene) as an example of an alkylation agent, it contains actual examples that illustrate only the use as alkylating agents in the method disclosed therein of polyalkylbenzenes where the alkyl groups are larger than methyl groups and indicates as follows that polyalkylbenzenes with alkyl groups other than methyl groups afford benefits in the method disclosed therein: "Polyalkylbenzenes with ethyl, propyl, or butyl groups with high-carbon alkyl groups have high reaction rates . . . . " Moreover, this published Japanese patent application states that when the naphthalene is solid at the reaction temperature, a solvent such as a paraffin or cycloparaffin should be employed. This published patent application publication discusses the use of halogenated alkyl in the alkylation of naphthalenes as a prior art method which did not produce a beta-alkyl naphthalene with the desired selectivity.
Shimada et al., "Ethylation and Transethylation of Naphthalene," Bulletin of the Chemical Society of Japan, Vol. 48 (II), pages 3306-3308 (Nov. 1975), disclose the transethylation of naphthalene by ethylbenzene or ethylxylenes to form monoethylnaphthalenes in the presence of an aluminum chloride catalyst at 20.degree.-30.degree. C. The rates of transethylation with ethylxylene isomers were reported to decrease in the order of 1,2-dimethyl-4-ethylbenzene.gtoreq.1,3-dimethyl-4-ethylbenzene .gtoreq.1,4-dimethyl-2-ethylbenzene .gtoreq.1,3-dimethyl-5-ethylbenzene.
Thus, until recently, no existing method was known for the highly selective production of 2,6diethylnaphthalene or a mixture of 2,6- and 2,7diethylnaphthalenes by a transethylation process. Then Hagen et al., U.S. Pat. No. 4,873,386, which issued on Oct. 10, 1989, disclose a method for producing 2,6-diethylnaphthalene which comprises: reacting in the liquid phase at least one of naphthalene or 2ethylnaphthalene as the feed with at least one of 1,4-diethylbenzene, 1,2,4-triethylbenzene, or at least one tetraethylbenzene or pentaethylbenzene as the ethylating agent per mole of the feed, in the presence of a Lewis acid catalyst selected from the group consisting of aluminum chloride, aluminum bromide, boron trichloride, tantalum pentachloride, antimony pentafluoride, and red oil at a level of from about 0.01 to about 1 mole of the catalyst (for red oil, based on the aluminum chloride content of the red oil) per mole of the feed and at a temperature in the range of from about -10.degree. C. to about 100.degree. C. In particular, Hagen et al., disclose that 1,2,3,4 - and 1,2,3,5-tetraethylbenzenes, as well as 1,2,4,5tetraethylbenzene (durene), are useful ethylating agents, but that hexaethylbenzene is not. Hagen et al. further disclose that 2,6-diethylnaphthalene is formed at a higher selectivity and yield when 2-ethylnaphthalene is transethylated and that pentaethylbenzene and any tetraethylbenzene are the preferred ethylating agents. However, Hagen et al. neither disclose nor suggest that the method disclosed therein would be useful for the selective methylation to produce p-alkyltoluene or 4,4'-alkylmethylbiphenyl.